Does Cow Temperament Affect Fertility?

Selecting cattle for mild temperament can pay off in a number of ways, in addition to handler safety, and based on results of a recent Kansas State University study, more docile cattle might provide an advantage in reproduction.

The K-State researchers designed their trial to analyze phenotypic relationships between docility and first-service AI conception rates in heifers. They collected data on 337 heifers from three cooperator herds in Kansas, with measurements including chute scores, exit velocity from the chute, fecal cortisol and blood-serum cortisol, along with heifer weight and age and 30-pregnancy following AI. Pregnancy rates among the three herds ranged from 34% to 60%.

In this trial, blood cortisol positively correlated with exit velocity, negatively correlated with age and tended to be negatively correlated with body weight. Older, heavier animals generally had better temperament, as indicated by lower blood cortisol, exit velocity and chute scores.

Statistically, the researchers did not measure significant differences showing direct relationships between docility and pregnancy rates when the data were combined from the three ranches. However, when they looked at data from each individual ranch, they found that on one of the ranches, chute scores and body weight were significant predictors for 30-day pregnancy rates. On that ranch, based on odds ratio estimates, a 1-unit increase in average chute score would reduce the probability of pregnancy on the ranch by 48%.

On that ranch, weight had a negative impact on pregnancy, and the researchers estimate that a 1-kg increase in body weight at breeding would decrease the probability of pregnancy by 2.2%.

The researchers note that while fertility is a complex trait dependent on multiple factors, their result, long with considerable variation in measures of temperament and reproductive status at all locations, indicates room for improvement in these traits. “Interactions between temperament and reproductive success merit further investigation and could prove conclusive with a data set of sufficient size,” they conclude.